Using this command line tool, you can control all LEDs connected to the LAN9512 or LAN9514 ethernet USB controller.
To access the registers of the LAN9512/LAN9514 chip via USB, you need to run the command as root:
This command would turn off the yellow SPD and the green LNK/ACT LED of an Raspberry B+ or Raspberry 2. The older Raspberry B also features an DUPLEX LED (I don't know which colors have the LEDs on the older Raspberry B).
For the Raspberry Pi 3 B+ you need an other program, lan7800-led-ctl, as the Raspberry Pi 3 B+ uses a different type of ethernet-controller.
You need to have cmake and libusb-1.0 installed (depending on your distro maybe also libusb-dev). Just call ./compile.sh
The source can be found on my git repo: lan951x-led-ctl.git